Abstract

The enormously destructive tsunami of December 2004, caused by sudden motion of the Sunda megathrust beneath the Indian Ocean, raised concerns about tectonically induced tsunami worldwide. Submarine landslides may also trigger dangerous tsunami. However, the potential and repeat time for such events is in most places poorly known due to inadequate exploration of the sea floor and age constraints. The high sediment flux and tectonic subsidence rate of the Malacca Strait-Mergui Basin shelf margin NE of northernmost Sumatra provide a favorable environment to generate and preserve submarine landslides. From ten seismic reflection profiles acquired in 2006, we identify three sediment packages that exhibit sliding characteristics such as headscarps, distorted beds and debris-toe structures. We assign lowstand marine isotope stages to the paleo-shoreline indicators observed in the profiles. We then determine the ages of these submarine landslides as 20–30 ka, 342–364 ka and 435–480 ka by the paleo-shoreline indicators that bound the top and bottom of the slide bodies. This sequence-stratigraphic approach shows that these events occurred near times of sea-level lowstands, which implies that a large amount of direct sediment influx during glacial periods is an essential precondition for basin-margin submarine landsliding. Spatiotemporal variations of sediment input due to lobe switching or Asian monsoon intensity changes also control basin-margin instability. Because we are currently at a highstand stage, and sediment flux to the continental margin is relatively small, so the chance of having a repeat submarine landslide and landslide tsunami along this basin-margin is low.